The present invention relates to methods of preparing medically useful radioisotopes, particularly high specific activity radioisotopes, and more particularly to methods of preparing high specific activity platinum- 195m (195mPt).
There is broad interest, from dosimetric perspectives, on the use of Auger-emitting radioisotopes coupled to specific cellular/nuclear targeting vectors for cancer therapy. The highest radiobiological effectiveness (RBI) results when Auger emitters are incorporated into the highly radiosensitive cell nucleus. Tumor cell-targeted agents radiolabeled with 195mPt could offer new opportunities for cancer therapy by high linear energy transfer (LET) Auger electrons, but 195mPt is not currently available in sufficiently high specific activity.
Accordingly, objects of the present invention include: provision of high specific activity platinum-195m (195mPt), provision of a high specific activity Auger-emitting radioisotope for coupling to specific cellular/nuclear targeting vectors for cancer therapy. Further and other objects of the present invention will become apparent from the description contained herein.
In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a new composition of matter that includes 195mPt characterized by a specific activity of at least 30 mCi/mg Pt.
In accordance with another aspect of the present invention, high-specific-activity 195mPt, is made by a method that includes the steps of: exposing Irridium-193 (193Ir) to a flux of neutrons sufficient to convert a portion of the 193Ir to 195mPt to form an irradiated material; dissolving the irradiated material to form an intermediate solution comprising Ir and Pt; and separating the Pt from the Ir by cation exchange chromatography to produce high specific activity 195mPt.